Two graphs illustrate why many financial analysts are concerned. The first shows the steep climb in debt under Obama.

The second shows the sharp rise in total U.S. credit market debt, including household debt and credit card debt, that has occurred since the 1980s. The total U.S. credit market debt hit a high of approximately 385 percent of U.S. Gross Domestic Product in 2009-2010 during the recession brought on by the collapse of the U.S. subprime mortgage market at the end of President George W. Bush’s second term in office.

The graph shows the ratio of total U.S. credit market debt to the GDP has fallen off in recent years, down to a current level of about 355 percent of GDP.

Among the many concerns is that the staggering increase in U.S. national debt evident over the past eight years has limited the ability of the federal economy to stimulate the economy. Typically, monetary policy has employed deficit spending, a tool popular with economists who follow Keynesian principles of economic theory.

Russia, China and Brazil each sold off at least $1 billion in treasury bonds in March, a month in which all central banks sold a net $17 billion.

The biggest month was January when central banks sold a record $57 billion in U.S. Treasury debt, with the global bank dump reaching a total of $123 billion so far this year.

CNN Money noted it’s the fastest pace for a U.S. debt selloff by global banks since at least 1978, according to U.S. Treasury data published this week.

CNN Money speculated that judging by the size of the selloff, policymakers within central banks have panicked over the dramatic drop in oil prices, compounded with concerns about China’s economic problems.

Selling U.S. Treasuries is one method central bankers can use to prop up the value of national currencies, many of which have lost value against the surprising continued strength of the U.S. dollar on international currency exchanges.

As a result, budget deficits rose, totaling $5.6 trillion in the five years between 2008 and 2012. Four of the five years had budget deficits larger in relation to the size of the economy than any budget deficit since 1946, the year immediately after the end of World War II.

The CBO concluded that the federal debt held by the public nearly doubled during this period. In 2015, the federal debt held by the public was equivalent to 74 percent of U.S. GDP, a higher percentage than at any point in U.S. history, except for a seven-year period around World War II.

The CBO further projected that with the continued aging of the population and the rising of health-care costs, the federal deficit will grow from less than 3 percent of GDP in 2015 to 6 percent in 2040, at which point the federal debt held by the public would exceed 100 percent of GDP – a level considered by many traditional economists to be seriously detrimental to U.S. economic growth.

On Jan. 25, 2016, the CBO reported the federal budget deficit had increased after six years of decline, to a total of $544 billion for 2016, $130 billion more than the CBO had projected in August 2015.

Mandatory spending, largely for entitlement programs such as health care and contributory programs such as Social Security, now accounts for 60 percent of the federal budget, with no limit in sight. More than 60 percent of the growth in mandatory spending projected in 2016 was for health care programs, including Medicare and Medicaid.

The CBO further projected that federal expenditures would remain at 21 percent of GDP for the next few years, higher than the average of 20.2 percent over the last 50 years.

“Because of rising interest rates and growing federal debt held by the public, the government’s interest payments on that debt are projected to rise sharply over the next 10 years – more than tripling in nominal terms and more than doubling as a percentage of GDP, from 1.4 percent to 3 percent,” the CBO estimated.

“Interest rates are now very low by historical standards, so net outlays for interest (in nominal dollars) are similar to their levels 15 to 20 years ago, even though federal debt now equals a considerably larger share of the economy,” the CBO report continued. “As interest rates rise, the government’s cost of financing its debt will climb – especially if that debt continues to mount, as it does in CBO’s projections.”

Fed ends ‘quantitative easing’ policy

In October 2014, the Fed under Janet Yellen’s direction ended the policy of quantitative easing under which it had purchased $85 billion in Treasury bonds every month in 2013. The policy culminated in what turned out to be 37 consecutive months during which the Fed bought Treasury debt in an effort to stimulate the economy by keeping interest rates at or near zero.

Under the QE bond-buying spree, the Fed balance sheet ballooned to a record $4.48 trillion accumulated since announcing the first round of QE purchases in November 2008 just as outgoing President George W. Bush tried to deal with a systemic collapse of financial markets.

The moves then helped propel Barack Obama into the White House as the housing market bubble fueled by speculative mortgages issued below investment grade collapsed.

Yellen assumed the Fed chair on Jan. 6, 2014, determined to “taper” QE borrowing down to zero by the end of 2014, a goal she achieved last October.

Given the increase in the national debt and the ballooning of the Fed balance sheet by more than $4 trillion in U.S. Treasury purchases, economists are concerned that the Fed could not easily resume a monetary policy of buying U.S. debt to fund the growing budget deficits projected by the CBO.